Melamine formaldehyde resins are extensively used for impregnating print and overlay sheets in the manufacture of decorative laminated plastics because of their transparency, toughness, light stability, and relatively low cost. Despite the widespread use of melamine formaldehyde resins as surface material, in decorative high-pressure laminates, these resins have one major deficiency in that they are quite brittle in an unmodified state. This brittleness limits their use in the preparation of decorative high-pressure postforming-type laminates. A postformable laminate is a fully cured laminate which can nevertheless be heated and bent into a new shape.
Fraser, in U.S. Pat. No. 2,817,614, noting the problems associated with flow promoting agents, such as polyesters and polyethylene glycol, in non-aqueous melamine compositions where they were not chemically combined with the melamine component, and the problems associated with aromatic amines and aromatic sulfonamides which are reacted with melamine and an aldehyde in an aqueous system; used an aralkyl quanamine as a modifying agent to improve postformability of laminates having melamine aldehyde impregnated surface layers. In Fraser, standard postforming to a 3/8 inch bend required temperatures of from 180.degree. C. to 200.degree. C.
Subsequently, McCaskey and Brooker, in U.S. Pat. No. 4,046,937, used water-soluble, aliphatic diglycidyl ethers as modifying agents to improve low temperature postformability of laminates having melamine aldehyde impregnated surface layers. Use of these modifiers allowed 1/4 inch postformability at about 121.degree. C. to 125.degree. C. There is a need, however, for even more improved postformable laminates and postforming resins providing an improved degree of toughness, clarity, water resistance, light stability, and postformability to laminate surface layers.